Biology lesson on the topic "structural features of a prokaryotic cell." Method for producing cellulose powder with a porous structure Questions for scientific secretaries

End. See No 5/2002

The cell is structural and
functional unit of living things

(General lesson in the form of a business game in 10th grade)

Fourth round. "I ask questions"

Teacher. This round can be defined as an intellectual duel between teams. Teams take turns asking each other questions about cell organelles.

"Prokaryotes." What is selective membrane permeability? ( The cell membrane is permeable to some substances and impermeable to others.)

"Eukaryotes". What are the types of endoplasmic reticulum (ER) and how do they differ? ( Smooth and rough EPS; the rough one has ribosomes, but the smooth one does not.)

"Prokaryotes." What functions does the EPS perform? ( Divides the cytoplasm into compartments, spatially separates chemical processes, transports proteins (rough ER), synthesizes and transports carbohydrates and lipids.)

"Eukaryotes". Why are ribosomes classified as non-membrane organelles? ( Ribosomes are made of protein and rRNA and do not have a membrane..)

"Prokaryotes." How did the Golgi apparatus get its name? ( Intracellular structures, later called the Golgi apparatus, were discovered in 1898 by the Italian scientist Camillo Golgi(1844–1926 ); Nobel Prize 1906)

"Eukaryotes". How do lysosomes relate to the Golgi apparatus? ( One of the functions of the Golgi apparatus is the formation of lysosomes.)

"Prokaryotes." What is the role of lysosomes in the cell? ( Digestion of substances entering the cell, destruction of unnecessary structures in the cell, self-destruction of the cell, if necessary.)

"Eukaryotes". What types of plastids are there? ( Green - chloroplasts containing chlorophyll and carotenoids and carrying out photosynthesis; yellow-orange and red chromoplasts involved in the synthesis of starch, oils and proteins; colorless – leukoplasts producing carotenoids.)

"Prokaryotes." List the organelles of movement. ( Microtubules, cilia, flagella.)

"Eukaryotes". What is the core? ( Double-membrane organelle consisting of a nuclear envelope with pores, chromatin, nucleolus and nuclear sap.)

"Prokaryotes." What organelle is in plant cell the biggest? ( Vacuole.)

"Eukaryotes". Why are there fewer mitochondria in a plant cell than in an animal cell? ( Animals are capable of active movement, therefore their energy costs are higher than those of plants, which affects the number of mitochondria.)

Teacher. You are well equipped with knowledge about the structure and functions of cell organelles. Let us now move on to the processes occurring in the cell.

Fifth round. "I Hear About a Cage"

Teacher. You will be presented with definitions of cell structures or processes that occur in a cell. It is necessary to choose the correct terms for them. You are given the right to choose: the correct answer to the question on the red card is scored “5”, on the green card – “4”.

"Prokaryotes." The living contents of eukaryotic cells, consisting of a nucleus and cytoplasm with organelles. ( Protoplasm.)

"Eukaryotes". Contents of a cell excluding the plasmalemma and nucleus. ( Cytoplasm.)

"Prokaryotes." The outer layer of animal and bacterial cells, consisting of polysaccharides and proteins, performing a mainly protective function. ( Glycocalyx.)

"Eukaryotes". A porous structure made of cellulose, hemicellulose and pectin substances, giving the cell strength and permanent shape. ( Cell wall.)

Teacher. Now let's do the opposite: I name and show the concept, and you give it a definition.

"Eukaryotes". Endocytosis is... ( Absorption of substances by a cell due to the formation of invaginations or their capture by membrane outgrowths.)

"Prokaryotes." Exocytosis is... ( Excretion from the cell various substances– hormones, undigested residues, etc..)

Questions for scientific secretaries.

1. What are the types of endocytosis? ( Pinocytosis, phagocytosis.)
2. Pinocytosis is... ( Absorption of liquid droplets by a membrane is characteristic of fungal, plant and animal cells.)
3. Phagocytosis is... ( Absorption of living objects and particulate matter by the cell through the formation of vesicles plasma membrane– characteristic of leukocytes that absorb bacteria, as well as amoebas.)

Teacher. You have successfully completed the fifth round, choosing the right definitions for the terms. Now let's test your observation skills.

Sixth round. "I'm Watching the Cell"

Teacher. Before starting the tasks of the sixth round, scientific secretaries are given the opportunity to prove themselves once again - to complete the tasks proposed on the board.

1st Secretary. Explain the structure and functions of mitochondria.

2nd secretary. Explain the structure and functions of cell chloroplasts.

3rd Secretary. Talk about the classification of cell organelles.

4th Secretary. Write down on the board the names of the organelles indicated by numbers on the “Cell” manual.

After the scientific secretaries complete the tasks, each team is offered a video about the process taking place in the cell. The teams' task is to determine what the process is and answer the question.

"Eukaryotes". Video "Cyclosis in a cage." What is cyclosis?

"Prokaryotes." Video "Cell division - mitosis." What is the significance of mitosis in a cell?

Teacher. Well, you coped with this task perfectly. In the next round you will play the role of researchers.

Seventh round. “I compare and make connections”

1. Two representatives from the team establish a connection between the structure and functions of the cell. You are offered micropreparations, after studying them using a light microscope, you need to determine: what is the peculiarity of tissue cells, what functions is this related to; name the tissue being studied. Remember the rules for working with a microscope and slides. The children are offered microslides “Geranium leaf epidermis”, “Human blood”, “Striated muscles”, “Bone tissue”.

2. Teams receive tables that present comparative characteristics plant and animal cells. Only in eukaryotes the column “Features of animal cells” is not filled in, and in prokaryotes the column “Features of plant cells” is not filled in. You have to restore scientific data - fill in the empty column. The “Structure of a Cell” manual will help you with this. Please get to work. Place the completed tables on the table of the scientific secretaries. They will check them and give their review.

3. At this time, let us turn to the scientific secretaries. Each academic secretary evaluates the work of his partner.

4. We give the floor to researchers who worked with microscopes. Each researcher gives a brief report on the work done.

So, the seventh round has been completed; for some of you, the research skills acquired at school will help you in the future when studying other sciences. After all, the same laws of Nature apply on our Earth. However, in any science there are rules, but there are also exceptions.

Eighth round. "I'm making an exception"

1. What is the exception when studying cellular structure organisms can be made? What organisms does it belong to? ( Viruses.)

3. How does a person assess the importance of viruses? Give examples. ( Cause viral diseases of plants, animals, humans.)

Ninth round. "I draw conclusions"

"Eukaryotes". So why is a cell the structural unit of an organism? ( All living organisms are made up of cells. The cell is one of the levels of life organization. There are no non-cellular forms of life, and the existence of viruses only confirms this rule, since they can manifest their properties of living systems only in cells.)

"Prokaryotes." Why is a cell the functional unit of an organism? (Because all properties of life: metabolism, growth, reproduction, development, irritability, discreteness, nutrition, excretion, autoregulation and rhythm are manifested in the cell.)

Scientific secretary. I would like to add: the cell is also the unit of development of organisms living on Earth. After all, changes that occur in it (for example, mutations) can lead to modifications.

Teacher. After talking with you for several lessons, I realized how interested you were in this unique topic. The logical conclusion of our lesson will be an essay on the topic “Poem about a Cell”, which you wrote yourself. I suggest reading this poem using creative homework.

(Students read their poems, and the academic secretary “makes” on the board a cell from “organoids” made independently by the students at home.)

DESCRIPTION

INVENTIONS

Union of Soviets

Socialistically

State Committee

USSR for Inventions and Discoveries

P. P. S. S., T. V. Vasilkova, V. A. A. A. A. Y. and L. I. Dernovaya (Institute organic chemistry AH of the Kirghiz SSR and the Order of the Red Banner of Labor inssTitut physical chemistry USSR Academy of Sciences (71) Applicants (54)METHOD FOR OBTAINING CELLULOSE POWDERS

WITH A POROUS STRUCTURE

However, this method is used to obtain. samples with low specific surface area. – up to 20 m9/g. 20

The table shows the specific surface area of powdered celluloses obtained by known and proposed methods.

The invention relates to the production of cellulose powders with a highly developed porous structure and can be used in preparative, analytical and biochemistry, chemical industry and technology.

The closest to the proposed invention in technical essence is a method for producing microcrystalline powdered cellulose by treating with 0.1-1% solutions of Lewis acids in neutral or proton-donor solvents and subjected to heat treatment at 70-100 ° C for 1-3 hours, with further heating - 15 washing and drying the target product Q. .

The purpose of the invention is to obtain cellulose powders with a highly developed porous structure.

To achieve this goal in the method of producing cellulose powders with a porous structure by treating cellulose with Lewis acids and subsequent heat treatment, washing and drying, the treatment is carried out

10-15 minutes at boiling, and after drying, the resulting powder is kept for 3060 minutes at 100-110 C. The resulting powdered cellulose has a more developed porous structure, and therefore a larger specific surface area, than known powdered cellulose sorbents.

Measurement of the specific surface area of samples - S- is carried out using the gas chromatographic method of retained volumes when n-hexane is used as vapor. Powdered cellulose obtained by hydrochloric acid hydrolysis is used as a standard. Its specific surface area, determined by the static method, is 1.7 m1/g.

The data indicate a significant increase in the specific surface area of cellulose powders formed using the proposed method.

Destructive acid

Type of cellulose sample t

20 (after warming up) 100

Cellulose obtained according to the known

Cellulose,. obtained using the proposed method

Formula of invention

TiCi4 108 135 220.

BF ° OE1 19 10 142

The determining factor that significantly affects the structure of the cellulose preparation is sample heating. The proposed method for producing cellulose powder leads to the appearance of numerous capillaries and pores in the product, penetrating the entire cellulose structure, which contributes to the formation of a large internal surface.

The powdered cellulose obtained by the proposed method is characterized by a maximum degree of polymerization

100-150 glucose units; and the content of carboxyl and reduced-. pouring carbonyl groups does not exceed 1 and 0.4%, ash content is less

1b. The main fraction of cellulose particles in length is within 0.25-0.5 mm and is about 95%.

Example 1. A sample of air-dried cellulose (20 g) is boiled for 15 minutes in 1000 ml ethyl alcohol and 2.7 ppm of titanium tetrachloride (0.2 mol per 1 cellulose anhydrous unit), pressed to three times the weight gain of the original sample and subjected to heat treatment for

1.5 h at 105 C. The product is then washed with vigorous stirring with ethanol, water, ethanol and air dried. Specific surface op. separated on a gas chromatograph

"Tsvet-100" uses n-hexane vapor as an adsorbate, column length 100 cm, sorbent mass

0.38 g, carrier - helium, flame ionization detector.

The specific surface area is 220 m Angle. Product output

97.2%; SP p= 100; ash content 0.86%.

0.2b; COOH 0.12%.

Example 2. The original cellulose is boiled for 10 minutes in 500 ml

Order 4658/31 Circulation 53

Branch of PPP "Patent", r. ethanol solution of stannous tetrachloride containing 1.8 ppm Lewis acid, which is

0.25 mol per 1 cellulose anhydrous unit. Next, the cellulose is placed in a drying oven for 1 hour at 110 C, having previously been squeezed out to a 2.8-fold increase in the weight of the sample. At the end of the heat treatment, the product is washed until neutral with ethanol, water, ethanol. Drying is carried out in air. The specific surface area, determined by the retained volume method, according to the method specified in example 1, is equal to 95 m1/g. The cellulose powder is then heated for

30 minutes at 110 and cool. S

500 m/yr. Product yield 97.3b| (P = 110; CHO and COOH groups 0.09 and 0.5b, respectively, Example 3. Natural cellulose fibers (25 g) are destroyed by boiling for 15 minutes in the presence of a solution of BFB ° OEt in ethanol

5.4 ml of acid and 500 ml of alcohol, pressed to 2.5-fold increase in

weighed and kept for 1.5 hours at 110, washed from the acid with a portion of ethanol, water, ethanol and dried in air.

The specific surface area, determined by the method described in example 1, 30 before heating is 19.5 m/r. After 1 hour

2 warm-ups at 105 the specific surface area increases to 150 m/g.

Product yield 96.6b; SP = 130.

Ash content 0.77%.

35 Suggested by cnocoai. The formation of powdered cellulose makes it possible to obtain samples with a highly developed porous structure and a large specific surface area, which exceeds this value compared to known cellulose powders by more than 10 times, relatively quickly and using simple technology.

Method for producing cellulose powders with a porous structure by treating cellulose with Lewis acids

50 with subsequent heat treatment, washing and drying of the target product, characterized in that, in order to obtain powders with a highly developed porous structure, 55 the treatment is carried out for 10-15 minutes at boiling, and after drying, the resulting powder is kept for 30-60 minutes at OO- 110 C.

Sources of information taken into account during the examination

Target: continue the formation of evolutionary ideas about development organic world and its division into prokaryotic and eukaryotic organisms; develop knowledge about prokaryotic cells.

Equipment: handout on the topic: “Structural features of a prokaryotic cell,” textbook drawings.

Lesson progress

I.Repetition and testing of knowledge of the studied material.

1. Oral survey. Structure and functions of the nucleus.

2. Written work on options. The questions are written on the board.

I Option.

Protein synthesis occurs on the (ribosome).
Structures that provide cell movement (cilia and flagella).
Cellular structure, containing genetic material in the form of DNA (nucleus).
Cell organelles in which carbohydrate synthesis occurs (plastids).
Single-membrane structures with enzymes that break down substances (lysosomes).

II Option.

The system of membranes that divides the cell into separate compartments in which metabolic reactions occur is called (EPS).
Stacks of membrane cylinders, vesicles, into which substances synthesized in the cell are packaged (Golgi complex).
Double-membrane cell organelles where energy is stored in the form of ATP molecules (mitochondria).
A porous cellulose structure that gives the cell strength and a permanent shape (cell wall).
The main substance of the cell, which contains all the organelles of the cell (cytoplasm).

II. Learning new material.

What are the levels of cellular organization?

What cells are called prokaryotic?

What organisms are prokaryotic?

Prokaryotic organisms retain traits the deepest antiquity: They are very simply designed.

Bacteria are typical prokaryotic cells. They live everywhere: in water, in soil, in food. Bacteria are primitive forms of life, and it can be assumed that they belong to the type of living creatures that appeared on the most early stages development of life on Earth.

Apparently, bacteria originally lived in the seas; Modern microorganisms probably originated from them. Man became acquainted with the world of bacteria relatively recently, only after they learned how to make lenses that provide sufficiently strong magnification. Technological developments in subsequent centuries made it possible to study bacteria and other prokaryotic organisms in detail.

The sizes of bacteria vary widely: from 1 to 10-15 microns.

Look at the pictures depicting bacteria. What shape can they have?

According to their shape, spherical cells are cocci, elongated cells are rods or bacilli, and convoluted cells are spirilla. Microorganisms can exist either individually or form clusters.

Bacteria can live either only in aerobic or only in anaerobic conditions, or both. They obtain the necessary energy through the process of respiration, fermentation or photosynthesis.

What structural features of bacteria can be identified?

The main structural features of bacteria are the absence of a nucleus limited by a shell. The hereditary information of bacteria is contained in one chromosome. The bacterial chromosome, consisting of one DNA molecule, has the shape of a ring and is immersed in the cytoplasm. The bacterial cell is surrounded by a membrane that separates the cytoplasm from the cell wall. There are few membranes in the cytoplasm. It contains ribosomes that carry out protein synthesis. Bacteria reproduce by dividing in two. Sometimes reproduction is preceded by a sexual process, the essence of which is the emergence of new combinations of genes in the bacterial chromosome. Many bacteria tend to form spores. Disputes arise when there is a lack of nutrients or when metabolic products accumulate in excess in the environment. Life processes inside the spores practically stop. Bacterial spores are very stable in a dry state. In this state, they remain viable for many hundreds and even thousands of years, withstanding sharp temperature fluctuations. Getting into favorable conditions, the spores transform into an active bacterial cell.

Write down the structural features of bacteria in your notebook.

Student’s presentation on the topic “The role of bacteria in nature and human life.” The rest of the students write a short summary.

Why is quarantine declared at school for some illnesses, but not for others? What rules for preventing infectious diseases do you know?

III. Consolidation and generalization of the studied material.

On each table there is material with tasks.

On the desks there are mixed complexes of drawings of organelles, chromosomes, nuclei and surface apparatus of cells. Fold a model of a prokaryotic cell. (One student makes a model at the board. Discussion of the results obtained.) Write a story about a prokaryotic cell, taking turns naming one of the features of its structure and life activity.

IV. Homework.

Features of the structure of a prokaryotic cell.

Literature:

Biology lessons in 10 (11) grade. Detailed planning. – Yaroslavl: Development Academy, 2001
General biology. 10-11 grades. V.B Zakharov, S.G. Mamontov, V.I. Sonin. – M. Bustard - 2002

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Report on chemistry on the topic:

Cellulose

Completed by a 10th grade student

Secondary school in Dubki village

Aglabova Maryam

Cellulose

Cellulose, fiber, main building material flora, forming the cell walls of trees and other higher plants. The purest natural form of cellulose is cotton seed hairs.

Purification and isolation.

Currently, only two sources of cellulose are of industrial importance - cotton and wood pulp. Cotton is almost pure cellulose and does not require complex processing to become a starting material for man-made fibers and non-fiber plastics.

After the long fibers used to make cotton fabrics are separated from the cotton seed, short hairs, or “lint” (cotton fluff), 10-15 mm long, remain.

The lint is separated from the seed, heated under pressure with a 2.5-3% sodium hydroxide solution for 2-6 hours, then washed, bleached with chlorine, washed again and dried. The resulting product is 99% pure cellulose. The yield is 80% (wt.) lint, the rest being lignin, fats, waxes, pectates and seed husks.

Wood pulp is usually made from the wood of coniferous trees. It contains 50-60% cellulose, 25-35% lignin and 10-15% hemicelluloses and non-cellulosic hydrocarbons. In the sulfite process, wood chips are boiled under pressure (about 0.5 MPa) at 140°C with sulfur dioxide and calcium bisulfite. In this case, lignins and hydrocarbons go into solution and cellulose remains.

After washing and bleaching, the purified mass is cast into loose paper, similar to blotting paper, and dried. This mass consists of 88-97% cellulose and is quite suitable for chemical processing into viscose fiber and cellophane, as well as cellulose derivatives - esters and ethers.

The process of regenerating cellulose from solution by adding acid to its concentrated copper-ammonia (i.e. containing copper sulfate and ammonium hydroxide) aqueous solution was described by the Englishman J. Mercer around 1844.

But the first industrial application of this method, which laid the foundation for the copper-ammonia fiber industry, is attributed to E. Schweitzer (1857), and its further development is the merit of M. Kramer and I. Schlossberger (1858).

And only in 1892 Cross, Bevin and Beadle in England invented a process for producing viscose fiber: a viscous (hence the name viscose) aqueous solution of cellulose was obtained after treating the cellulose first with a strong solution of caustic soda, which gave “soda cellulose”, and then with carbon disulfide (CS2 ), resulting in soluble cellulose xanthate.

By squeezing a stream of this "spinning" solution through a spinneret with a small round hole into an acid bath, the cellulose was regenerated in the form of rayon fiber.

When the solution was squeezed into the same bath through a die with a narrow slit, a film called cellophane was obtained.

J. Brandenberger, who worked on this technology in France from 1908 to 1912, was the first to patent a continuous process for making cellophane.

Chemical structure

Despite the widespread industrial use of cellulose and its derivatives, the currently accepted chemical structural formula cellulose was proposed (by W. Haworth) only in 1934.

True, since 1913 its empirical formula C6H10O5 has been known, determined from quantitative analysis of well-washed and dried samples: 44.4% C, 6.2% H and 49.4% O.

cellulose fiber viscose

Thanks to the work of G. Staudinger and K. Freudenberg, it was also known that this is a long-chain polymer molecule, consisting of those shown in Fig. 1 repeating glucosidic residues.

Each unit has three hydroxyl groups - one primary (- CH2CHOH) and two secondary (>CHCHOH).

By 1920, E. Fischer had established the structure of simple sugars, and in the same year, x-ray studies of cellulose first showed a clear diffraction pattern of its fibers. The X-ray diffraction pattern of cotton fiber shows a clear crystalline orientation, but flax fiber is even more ordered. When cellulose is regenerated into fiber form, crystallinity is largely lost.

How easy it is to see in the light of achievements modern science, the structural chemistry of cellulose practically stood still from 1860 to 1920 for the reason that all this time the auxiliary scientific disciplines necessary to solve the problem.

Regenerated cellulumOza

Viscose fiber and cellophane.

Both viscose fiber and cellophane are regenerated (from solution) cellulose. Purified natural cellulose is treated with an excess of concentrated sodium hydroxide; After removing the excess, the lumps are ground and the resulting mass is kept under carefully controlled conditions. With this “aging,” the length of the polymer chains decreases, which promotes subsequent dissolution. Then the crushed cellulose is mixed with carbon disulfide and the resulting xanthate is dissolved in a solution of sodium hydroxide to obtain “viscose” - a viscous solution. When viscose enters an aqueous acid solution, cellulose is regenerated from it. The simplified total reactions are:

Viscose fiber, obtained by squeezing viscose through small holes of a spinneret into an acid solution, is widely used for the manufacture of clothing, drapery and upholstery fabrics, as well as in technology. Significant quantities of viscose fiber are used for technical belts, tapes, filters and tire cord.

Cellophane

Cellophane, obtained by squeezing viscose into an acid bath through a spinneret with a narrow slot, then passes through washing, bleaching and plasticizing baths, is passed through drying drums and wound into a roll. The surface of cellophane film is almost always coated with nitrocellulose, resin, some kind of wax or varnish to reduce the transmission of water vapor and provide the possibility of thermal sealing, since uncoated cellophane does not have the property of thermoplasticity.

In modern production, polymer coatings of the polyvinylidene chloride type are used for this, since they are less moisture permeable and provide a more durable connection during heat sealing.

Cellophane is widely used mainly in the packaging industry as a wrapping material for dry goods, food products, tobacco products, and also as a base for self-adhesive packaging tape.

Viscose sponge

As well as forming a fiber or film, viscose can be blended with suitable fibrous and fine crystalline materials; After acid treatment and water leaching, this mixture is converted into a viscose sponge material (Fig. 2), which is used for packaging and thermal insulation.

Copper-ammonia fiber

Regenerated cellulose fiber is also produced on an industrial scale by dissolving cellulose in a concentrated copper-ammonia solution (CuSO4 in NH4OH) and spinning the resulting solution into fiber in an acid precipitation bath. This fiber is called copper-ammonia fiber.

Properties of cellulose

Chemical properties.

As shown in Fig. 1, cellulose is a highly polymeric carbohydrate consisting of glucosidic residues C6H10O5 connected by ether bridges at position 1,4. The three hydroxyl groups in each glucopyranose unit can be esterified with organic agents such as a mixture of acids and acid anhydrides with a suitable catalyst such as sulfuric acid.

Ethers can be formed by the action of concentrated sodium hydroxide leading to the formation of soda cellulose and subsequent reaction with an alkyl halide:

Reaction with ethylene or propylene oxide produces hydroxylated ethers:

The presence of these hydroxyl groups and the geometry of the macromolecule determine the strong polar mutual attraction of neighboring units. The attractive forces are so strong that ordinary solvents are not able to break the chain and dissolve cellulose.

These free hydroxyl groups are also responsible for the greater hygroscopicity of cellulose. Esterification and etherization reduce hygroscopicity and increase solubility in common solvents.

Under the influence aqueous solution acids break oxygen bridges at the 1,4- position. Complete breakage of the chain produces glucose, a monosaccharide. The initial chain length depends on the origin of the cellulose. It is maximum in its natural state and decreases during the process of isolation, purification and conversion into derivative compounds (see table).

Degree of cellulose polymerization

Even mechanical shear, for example during abrasive grinding, leads to a decrease in chain length. When the polymer chain length is reduced below a certain minimum value, the macroscopic physical properties of cellulose change.

Oxidizing agents affect cellulose without causing cleavage of the glucopyranose ring (Fig. 4). Subsequent action (in the presence of moisture, such as in climate testing) typically results in chain scission and an increase in the number of aldehyde-like end groups.

Since aldehyde groups are easily oxidized to carboxyl groups, the content of carboxyl, which is practically absent in natural cellulose, increases sharply under conditions of atmospheric influences and oxidation.

Like all polymers, cellulose is destroyed under the influence of atmospheric factors as a result of the combined action of oxygen, moisture, acidic components of air and sunlight.

The ultraviolet component of sunlight is important, and many good UV protective agents increase the life of cellulose derivative products. Acidic air components, such as nitrogen and sulfur oxides (and they are always present in atmospheric air industrial areas) accelerate decomposition, often with a stronger effect than sunlight.

Thus, in England, it was noted that cotton samples tested for exposure to atmospheric conditions in winter, when there was practically no bright sunlight, degraded faster than in summer.

The fact is that burning in winter large quantities coal and gas led to an increase in the concentration of nitrogen and sulfur oxides in the air. Acid scavengers, antioxidants, and UV absorbers reduce the weathering sensitivity of cellulose.

Substitution of free hydroxyl groups leads to a change in this sensitivity: cellulose nitrate degrades faster, and acetate and propionate - more slowly.

Physical properties. Cellulose polymer chains are packed into long bundles, or fibers, in which, along with ordered, crystalline ones, there are also less ordered, amorphous sections (Fig. 5). The measured percentage of crystallinity depends on the type of cellulose as well as the method of measurement. According to X-ray data, it ranges from 70% (cotton) to 38-40% (viscose fiber).

X-ray structural analysis provides information not only about the quantitative relationship between crystalline and amorphous material in the polymer, but also about the degree of fiber orientation caused by stretching or normal growth processes. The sharpness of diffraction rings characterizes the degree of crystallinity, and diffraction spots and their sharpness characterize the presence and degree of preferred orientation of crystallites.

In a sample of recycled cellulose acetate produced by the dry-spinning process, both the degree of crystallinity and orientation are very small.

In the triacetate sample, the degree of crystallinity is higher, but there is no preferred orientation. Heat treatment of triacetate at a temperature of 180-240 0 C noticeably increases the degree of its crystallinity, and orientation (by stretching) in combination with heat treatment gives the most ordered material. Len discovers high degree both crystallinity and orientation.

References

1. Bushmelev V.A., Volman N.S. Processes and apparatus for pulp and paper production. M., 1974

2. Cellulose and its derivatives. M., 1974

3. Akim E.L. and others. Technology of processing and processing of cellulose, paper and cardboard. L., 1977

4. http://bio.freehostia.com (Internet source)

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